(1) Field of the Invention
The present invention relates to a press machine structure provided to a bending machine with an upper die and a lower die, wherein a pad, which is suspended through a spring means from a ram having the upper die suspended therefrom, has a punch, while the lower die is provided with a die engageable with the punch. More particularly, the invention pertains to a press machine structure wherein the above-mentioned punch is connected with the above-mentioned pad through another spring means, while a push rod provided to the above-mentioned upper die has a step portion and faces the punch so that the punch can be pressed through the step portion so as to be able to advance to and retreat from the above-mentioned die.
(2) Description of the Prior Art
As is generally known, when the car body of an automobile is pressed, two processes, i.e., a bending process and a punching process, are necessary on the grounds of the structure of the body.
Accordingly, such a form has been devised and conventionally employed as follows. As shown in FIG. 1, first, in a bending operation as a first process, a work stock 4 having a portion 3 to be punched out is properly set on a lower die 2 of a press machine 1 as a bending press. Then, a ram 5 is lowered from the upper side. In consequence, a pad 8, which is suspended through compression springs 7, 7 as spring means from an upper die 6 suspended from the ram 5 and is projected from the upper die 6, presses the portion 3 to be punched out of the work stock 4. As a result, the portion 3 to be punched out is clamped between the lower die 2 and the pad 8 and at the same time, the upper die 6 contacts with the work stock 4 and presses the same to be plastically deformed and moreover, the upper die 6 brings the work stock 4 into pressure-contact with the lower die 2 to form a work 4' with a given shape.
Thereafter, the ram 5 is reset to a given posture, and the work 4' thus pressed is removed and carried to a punching press in the subsequent process, where the portion 3 to be punched out is punched out.
The conventional method, therefore, has such a problem that the process is complicated, since there is a need for two processes in working the work stock 4.
Moreover, there is such a problem that it is necessary to install a transfer apparatus and the like between the processes, so that the installation cost increases and the greatest care is needed for also the maintenance of the work 4' in the transfer course. As a result, the manhour increases, and consequently the cost becomes higher.
Furthermore, there is also such a disadvantage that the reproducibility of the working position of the work 4' set on the punching press in the subsequent process is bad, so that there is a need for a skill in setting of the work 4'.
It is a matter of course that such a form has been devised and employed for coping with the above-mentioned problems and disadvantages as follows. As shown in FIG. 2, a die 9 is integrally provided to a lower die 2' of a press machine 1', and a punch 10 engageable with the die 9 is mounted on an upper die 6' suspended from the ram 5, the punch 10 being projected from the upper die 6'. On the other hand, a pad 8' is fitted around the whole circumference of the punch 10, the pad 8' being further projected from the punch 10. Consequently, as the ram 5 lowers, the upper die 6' presses the work stock 4 set on the lower die 2' and at the same time, the pad 8' contacts with the work stock 4, thereby allowing the periphery of a portion 3' to be punched out of the work stock 4 to be clamped by the peripheral edge of the die 9 and the pad 8'. Then, the upper die 6' approaches to the lower die 2' in order to plastically deform the work stock 4 into a given bent shape and at the same time, the punch 10 lowers to punch out the portion 3' to be punched out, forming a hole, and engages with the die 9. The portion 3' to be punched out is discharged from a passage 12, as a punching scrap 3".
However, although the above-described form has such a merit that bending and punching are simultaneously effected, there is such a shortcoming that the fitting space of the pad 8' is regulated owing to the working design restrictions of the upper die 6' and the punch 10 and therefore, a satisfactory rigidity cannot be guaranteed in pressing the work stock 4, so that warpage may be produced at the peripheral edge of the hole in punching.
Moreover, there is also such a shortcoming that since punching is effected by an impact load, in bending a tensile stress is spread to the hole previously formed by punching, causing the hole to be deformed.